This invention relates generally to a rubber composition and more particularly concerns a rubber composition containing a phyllosilicate mineral filler.
The precise formulation of any rubber compound depends on its intended end use. Different end uses require very specific mechanical properties. To a degree, the choice of filler and agent for coupling the rubber and filler determines the mechanical properties of the rubber compound. For example, the use of organosilane coupling agents generally of formula I shown hereinbelow, in conjunction with phyllosilicate minerals as extending or reinforcing fillers in natural or synthetic rubber compositions, is well known in the art--especially as represented by Sample et al., U.S. Pat. No. 4,260,498, which in its entirety is specifically incorporated herein by reference. Alexander et al., U.S. Pat. No. 2,801,186 and Doran et al., U.S. Pat. No. 3,737,334 also contain illustrative disclosures. In such cases, the organosilane serves to improve the overall mechanical properties of the rubber compositions. In use, certain functional organic groups of the organosilane hydrolyze in the presence of moisture typically found on the surface of the minerals to form silanols which react with or otherwise condense in the presence of silica, clay or metal oxide surfaces. To be effective in this respect, the silane coupling agent must be reactive with both the rubber and filler. The coupling agent may be applied to the filler in a separate pretreatment step, or it may be added directly during compounding of the rubber.
Quaternary ammonium salts have also been disclosed for use with phyllosilicate mineral fillers or pigments. Technical Report 35-T entitled "Factors Affecting the Dispersion of Ultra-Fine Particle Size Mistron Talcs in Water and the Effects of Wetting and Dispersion Agents" and published in 1956 by Sierra Talc & Clay Company (now Cyprus Mines Corporation) describes quaternary ammonium salts as effective dispersants for talc in water. Technical Report 48-T entitled "Mistrons in Hydrocarbon Solvents--Effects of Cationic Surfactants" and published in 1958 by the former Sierra Talc & Clay Company describes certain quaternary ammonium salts as dispersants of talc in plastics, rubber and other polymeric dispersions. German Offenlegungsschrift No. 2,224,003 which issued in 1972 contains a very similar disclosure. E. K. Lotakova, G. A. Blokh, E. V. Tsipenyuk, I. G. Lebed, T. G. Blokh, F. D. Ovcharenko, N. G. Vasileo, A. D. Chugai and V. A. Mashchenko, "Properties of Rubbers Filled with Modified Kaolins," Kozh.-Obuvn. Prom-st. Vol. 18(6), pp. 45-7 (1976) discloses the reinforcement of rubbers with kaolin modified with benzyldimethylalkylammonium chloride. N. S. Gilinskaya, G. A. Sankina, M. S. Skorobogatova, "Effect of the Chemical Nature of Dihydric Phenols and Quaternary Ammonium Salts on the Properties of Vulcanized Rubbers Made from the Rubber SKR-26," Kauch. Rezina, Vol. 3, pp. 10-12 (1980) discloses the vulcanization of rubber in the presence of quaternary ammonium salts.
Brown, U.S. Pat. No. 3,024,126 discloses rubber compositions containing reinforcing silica, a silane and a quaternary ammonium salt. Mukamal et al., copending U.S. patent application Ser. No. 297,175 filed Aug. 28, 1981, discloses rubber compositions containing a phyllosilicate mineral, a silane of formula I below and a primary, secondary or tertiary amine having a specific structural formula.
The use of a phyllosilicate mineral filler in conjunction with both an organosilane and a quaternary ammonium salt has not heretofore been disclosed for use in rubber compositions. Furthermore, in spite of the known efficacy of organosilanes or quaternary ammonium salts in rubber compositions, efforts continue to discover alternatives or improvements to known organosilanes and quaternary ammonium salts in rubber compositions. A problem of using such additives as organosilanes in rubber compositions is their relatively high cost. It is therefore desirable to reduce the amount of such agents in rubber compositions without also reducing their effect on the mechanical properties of the rubber compositions.